The field of the present invention relates generally to a process for combusting a fuel containing sulfur to generate electricity through a gas turbine.
A gas turbine will combust a fuel and a compressed working gas, usually air, in a combustor to form a combusted stream which is expanded in a turbine to generate electricity. The fuel will typically be a hydrocarbon which contains carbon and hydrogen which are combusted with oxygen from the working gas by exothermic reactions to produce carbon dioxide and water, respectively. An example of one suitable fuel is natural gas. When the fuel to be used in a gas turbine contains sulfur, the fuel must be treated for sulfur removal prior to combustion to avoid pollution and corrosive problems associated with the sulfur.
In a typical sulfur treatment process, the fuel will be treated to form a sour gas stream and a purified fuel gas stream containing substantially no sulfur or sulfur compounds. The sour gas may then be treated to recover sulfur and a waste tail gas composed of carbon dioxide and trace amounts of contaminants such as hydrogen sulfide (H.sub.2 S) and carbonyl sulfide (COS). Because of pollution concerns, these compounds must normally be removed from the carbon dioxide before release to the atmosphere. Such removal may be accomplished by combusting the compounds with oxygen to form sulfur dioxide in an incinerator which is released through a smokestack to the environment. However, such combustion requires a fuel source to raise the temperature of the tail gas containing carbon dioxide to a level which will insure combustion of the sulfur compounds.
In a conventional process for combusting a fuel containing sulfur, a small stream of purified fuel gas will be diverted to the incinerator to combust the contaminant sulfur compounds. Since this diversion stream of purified fuel gas is not being used to produce electricity or work in the gas turbine, it is effectively "lost" and therefore reduces the overall efficiency of the power cycle.
One process for treatment of tail gas containing hydrogen sulfide is described in U.S. Pat. No. 4,331,630 to Van Pool. This process describes the combination of the fuel gas and the tail gas before they are introduced to the incinerator to accomplish acceptable combustion at a substantially lower stack temperature than previous processes. While this process substantially lowers the amount of fuel "lost" to sulfur pollution abatement, it still requires the use of fuel in the incinerator.
Accordingly, there exists a need for a process for combusting fuel containing sulfur, wherein the amount of clean fuel "lost" to pollution abatement is reduced, thereby increasing the overall efficiency of electricity generation from fuels containing sulfur. This need is especially acute for fuels containing a large amount of sulfur which require a correspondingly larger amount of "lost" fuel to incinerate the increased sulfur contaminants in the tail gas.